Organic light-emitting devices such as organic electroluminescence devices (organic EL devices) can be easily applied to surface light-emitting devices, whereby much attention has been paid to the new optical devices. The organic light-emitting devices are specifically considered to be useful as an economical, solid emission-type, full color display device having a large emission area, or a writing light source arrays, etc., and have been actively studied. The organic light-emitting devices generally comprise a couple of electrodes (a transparent electrode and a back electrode), and a light-emitting layer disposed between the electrodes. When electric field is applied to the electrodes, electrons are injected from the back electrode and holes are injected from the transparent electrode to the light-emitting layer. The electrons and the holes are re-combined in the light-emitting layer, and the organic light-emitting device emits light such that the energy is converted into the light while the energy level is turned from a conduction band to a valence band.
In the organic EL devices, it is important that the negative electrode and the positive electrode are excellent in charge injection properties. When the charge injection properties are lower, the organic EL device needs a higher driving voltage to be poor in energy efficiency and driving durability. The charge injection properties are affected by work functions of conductive materials contained in the electrodes. The negative electrode desirably contains a conductive material with a low work function, and the positive electrode desirably contains a conductive material with a high work function. Further, the conductive material contained in each electrode is desirably light-transmittable. At least one of the negative electrode and the positive electrode has to be transparent to view an image from at least one surface of the organic EL device. The negative electrode is generally opaque or translucent because only metal materials have been known as materials having a low work function and excellent electroconductivity. Thus, the positive electrode is generally a transparent electrode comprising a metal oxide such as indium tin oxide (ITO), etc.
However, the work function of common ITO is approximately 4.7 eV. Though the work function of ITO can be increased by a surface treatment, it is approximately 4.9 eV at most. Further, because ITO has higher electric resistance as compared with metals, a charge injection-type light-emitting device such as the organic EL device using ITO disadvantageously produces brightness unevenness and generates heat with lower display quality, particularly in the case of using a transparent electrode with a large area. Thus, ITO is insufficient in the electric resistance and the work function though it has been most preferably used for the transparent electrode of the organic EL device. High-conductive materials such as gold are sufficient in the electric resistance and the work function, however, gold is absolutely disadvantageous in the light impermeability.
Under such circumstances, an organic EL device, which comprises a low resistant metal bus line (metal film) patterned by photolithography and a transparent conductive layer disposed on the metal bus line, has been proposed in JP 10-12386 A, etc.
However, the metal bus line is light-impermeable and reduces the light-emitting efficiency of the organic EL device. Further, the patterning of the metal bus line needs complicated processes. Though the reduction of the light-emitting efficiency can be effectively prevented by thinning the lines of the metal bus line, technologies capable of producing a thinner network conductive material lines in a large area with reduced costs are not known.